docs: add warning about packageManager config

[capaj]

just something I bumped into today

[petebacondarwin]

I suspect we should be able to infer the package manager in use??

[Cherry]

@petebacondarwin This is inferred by #190 and then fixed in #193, and I'm not really sure the "default" copy/pasted config should use pnpm - that's definitely not the standard.

"The package manager you'd like to use to install and run wrangler. If not specified, the preferred package manager will be inferred based on the presence of a lockfile or fallback to using npm if no lockfile is found. Valid values are npm | pnpm | yarn | bun."

You do not need to specify packageManager as the docs now suggests, as long as you're running an up to date version.

[Cherry]

The detection of pnpm looks for a pnpm-lock.yaml file in the working directory, but only after looking for a package-lock.json, and then a yarn.lock.

If you have a pnpm-lock.yaml committed, and none of these other files, it should work as expected.

[IgorMinar]

Unfortunately this header makes all the following paragraphs appear as if they were part of the packageManager docs.